The spine is critical in human physiology for mobility, support, and balance. The spine protects the nerves of the spinal cord, which convey commands from the brain to the rest of the body, and convey sensory information from the nerves below the neck to the brain. Even minor spinal injuries can be debilitating to the patient, and major spinal injuries can be catastrophic. The loss of the ability to bear weight or permit flexibility can immobilize the patient. Even in less severe cases, small irregularities in the spine can put pressure on the nerves connected to the spinal cord, causing devastating pain and loss of coordination.
Surgical procedures on the spine often include the immobilization of two or more vertebra. Immobilizing the vertebrae may be accomplished in many ways (e.g. fixation plates and pedicle screw systems). One of the most common methods for achieving the desired immobilization is through the application of bone anchors (most often introduced into the pedicles associated with the respective vertebra to be fixed) that are then connected by rigid rods locked to each pedicle screw. These pedicle screw systems are very effective. Pedicle screws generally include an anchor component and a rod-housing component.
However, in some cases screws are not the best choice for a spinal bone anchor. Some bone structures might not have sufficient mechanical strength or integrity to withstand penetration by the screw, due to injury or age-related deterioration. In some cases it may be desirable for the bone anchor to have a small degree of freedom of movement relative to the bone structure, which cannot be provided by bone screws. Still in some other cases it may be desirable to provide stability to an adjacent vertebra or multiple vertebrae adjacent to a vertebra being immobilized with a fixation construct, yet without fully immobilizing the adjacent vertebra.
As a result there is a need in the art for alternative fastening means for bone anchors.